Utility furnaces and industrial boiler systems operating with atmospheric burners, like all hydrocarbonaceous fuel combustion systems, are concerned with the amount and quality of the emissions that result from the combustion of fuel in those systems. Particulate emissions are a byproduct of incomplete combustion. This carbon-containing particulate is an environmental issue, and to solve it, fuel compositions are constantly being modified and combustion methods designed to minimize the amount of particulate emitted into the environment. Other emission constituents can form deposits on various parts of the combustion system, for instance, the water wall pipes, economizer tubes, and/or super heater tubes of utility furnaces and industrial burner systems. The deposits, typically referred to as slag, may build up and, over time, significantly reduce the efficiency of the combustion system.
Metal-containing additives have been used in fuel formulations to catalyze carbon burn out, and thereby reduce particulate emissions, by either inhibiting particulate agglomeration (alkali metals), enhancing carbon oxidation at peak combustion temperatures by increasing hydroxyl radical concentration (alkaline earth metals), or by increasing the rate of catalytic oxidation by lowering the particulate light-off temperature (transition metals). It is recognized, however, that use of these specific metal-containing additives may adversely affect the type and/or quantity of slag that may build up in a combustion system.
In one example, the prior art discloses a method for reducing emissions which include the use of a mixture of calcium and either alkali metals, alkaline earth metals other than calcium or mixtures thereof. See U.S. Pat. No. 5,919,276.
It is also known that adding magnesium compounds to fuels extends the time between combustion turbine maintenance when burning ash-containing fuel. See, e.g., U.S. Pat. No. 6,632,257. However, magnesium does not impact carbon burnout. Magnesium compounds, therefore, positively affect the type and/or quantity of slag, but do not impact carbon burnout.